This invention relates to improved phenolic molding compositions and, in particular, to sheet molding compositions based on resole phenolic resins and having improved maturation characteristics.
Thermosetting phenolic molding compositions, based on phenol formaldehyde resins in admixture with fillers, are commonly used to form molded articles which can be readily cured into hard durable molded products. A typical phenolic molding composition is described in U.S. Pat. No. 2,424,787. The patent discloses the use of both "1-stage" or resole and "2-stage" or novolak resin in the production of phenolic molding compositions. In the production of the resole resin molding compositions, the patentee discloses that it is necessary to mix the resin syrup with the filler, because of the liquid nature of the resin. It is further taught that it is preferred to incorporate an alkali metal oxide or an alkaline earth metal oxide including compounds of calcium and magnesium, in the molding composition with the phenolic resin and filler. Magnesium oxide is mentioned as particularly advantageous. The addition of the oxide to the molding composition causes the composition to harden at room temperature or at slightly elevated temperatures. However, this solidification does not convert the resin into the final infusible, insoluble stage and the solidified product may be molded under heat and pressure to form a final molded product.
U.S. Pat. No. 4,075,155 to Philipps, discloses the use of phenol formaldehyde resole molding compositions in sheet molding compound (SMC) technology which heretofore had been generally limited to the use of polyester resins. The molding compositions of Philipps include fillers, compounds such as calcium hydroxide and magnesium hydroxide, mold release agents and coupling agents.
U.S. Pat. No. 3,956,227, discloses phenolic molding compounds including cement which contains calcium oxide and further disclosed the use of silane coupling agents. Sheet molding compounds were disclosed by the patentees. Related patents include U.S. Pat. Nos. 3,944,515 and 3,988,289. A later patent, U.S Pat. No. 4,182,701, was directed to phenolic molding compounds made by mixing the phenol and aldehyde reactants together with calcium hydroxide and a silane coupling agent. Use of calcium hydroxide and magnesium hydroxide during the reaction of the phenolic resin is also disclosed in U.S. Pat. No. 4,070,331.
Olivo et al in U.S. Pat. No. 4,116,921 disclose phenolic molding compounds made from formaldehyde and bisphenol. The patentees disclose the use of calcium oxide or hydroxide in the molding compounds. These patentees also disclose the use of hollow carbon and hollow phenolic resin microballoons.
British Patent No. 1,363,227 to Farkas discloses sheet molding compounds made from a phenol aldehyde resole resin that is modified with a glycol. The resins are cured with acids. Resins that are modified with oligomers are disclosed in U.S. Pat. No. 4,419,400.
There are several patent applications published in Japan, dealing with this technology. In an application published as Sho-56-92727, sheet molding compounds are disclosed which contain resole phenolic resins, calcium and/or magnesium hydroxides or oxides and fillers such as talc, clay and the like.
Japanese Patent Publication Sho-58-91935, discloses phenolic molding compounds which contain resole phenolic resins, a thickener, such as the oxides or hydroxides of calcium and magnesium, fillers and reinforcing materials combined with abrasive materials for use in brake shoes. Sheet molding compound technology is used in forming the brake shoes.
Japanese Publication Sho-59-170126 discloses sheet molding compounds made with resole phenolic resins, alkaline earth metal oxides or hydroxides impregnated into special configurations of continuous and discontinuous glass fibers.
Commercial sheet molding compositions, whether based on a polyester, phenol-formaldehyde, or other resin are typically formulated and mixed at a relatively low viscosity, for ease of mixing, combined with fiber reinforcement materials and formed as a sheet in a sandwich configuration between two polymeric films. The polymer films must be removed before the sheet molding composition can be molded to its final form. Generally, phenolic sheet molding compositions are oven-aged at 30.degree. to 60.degree. C. for a few days before the sheets can be removed by peeling from the phenolic composition. The oven-aging is a time consuming and expensive process. Accordingly, it is an object of the present invention to provide a phenolic sheet molding composition having improved aging or maturation properties, and requiring a shorter maturation time and little or no oven-aging before removing the polymer film.